An image processing apparatus which can rotate input image data in a compressed state, comprises a storage unit which stores a rotation angle of the image data; a holding unit which holds, for each tile including blocks each including a predetermined number of pixels in the image data, information on a color arrangement in the block obtained by compressing the image data, color information corresponding to the color arrangement, and information on a position of the tile in the image data; and a rotation unit which converts the color arrangement in the block in accordance with the rotation angle of the image data stored in the storage unit to form rotated image data based on the converted color arrangement, color information corresponding to the color arrangement, and information on a position of the tile.